Oxide cathode for an electric discharge tube

ABSTRACT

An oxide cathode having an oxide layer obtained from triple carbonate and a support obtained according to the powdermetallurgical method having a content of Si, Al and Ti lower than 0.005 percent by weight.

United States Patent Coenen et a].

Oct. 7, 1975 OXIDE CATI-IODE FOR AN ELECTRIC DISCHARGE TUBE Inventors: Renier Gertruda I-Iubertus Coenen,

Eindhoven; Karel Martin Hubert Leummens, Nijmegen; Erland Charles Justus Swaving, Eindhoven, all of Netherlands Assignee: U.S. Philips Corporation, New

York, N.Y.

Filed: May 30, 1974 App1. No.: 474,587

Foreign Application Priority Data June 6, 1973 Netherlands 7307855 11.5. C1 313/346 R; 313/311; 313/337 1111. 0. HOIJ 1 14; I-lOlJ 19/06 Field of Search 313/346, 352, 354, 311

Primary Examiner-Saxfield Chatmon, Jr. Attorney, Agent, or Firm-Frank R. Trifari; George B. Berka [57] ABSTRACT An oxide cathode having an oxide layer obtained from triple carbonate and a support obtained according to the powder-metallurgical method having a content of Si, Al and Ti lower than 0.005, percent by weight.

1 Claim, 1 Drawing Figure US. Patent 0ct. 7 ,1975 v 3,911,312

OXIDE CATIIODE FOR AN ELECTRIC DISCHARGE TUBE The invention relates to an oxide cathode for an electric discharge tube and in particular to such a cathode whose emissive layer consists of a mixture of oxides of barium, strontium and calcium and in which a good adhesion of the emissive oxide layer to a nickel cathode support is obtained.

A cathode having such an oxide layer is known from French Pat. Specification No. 1,107,589. The oxides of said layer are obtained from the carbonates. A mixture of the carbonates of the said metal is termed triple carbonate and comprises the said carbonates of barium, strontium and calcium, for example, in the weight ratio 7, 6, l. A drawback of such oxide layers formed from triple carbonate is that the adhesion to a nickel cathode support leaves to be desired.

A very good adhesion of an emissive oxide layer obtained in a triple carbonate can be obtained, if, according to the invention, the support consists of nickel obtained according to the known powder-metallurgical method which comprises reductors such as magnesium and/or carbon, but in which the silicon, aluminum and titanium content is lower than 0.005 percent by weight. Other impurities, such as chromium which may form an intermediate layer with the emissive layer should also be below said limit.

An oxide cathode in which a support is manufactured from nickel prepared according to the powder metallurgical method is known from French Pat. Specification No. 1,152,810. In this specification the Si content was maintained low with a view to the formation of a poorly electrical conducting layer between the oxide layer and the support, but nothing was stated about the Al and Ti contents. In connection with the adhesion said impurities were of little significance since the oxide layer contained barium oxide and strontium oxide only. Such a layer containing only two oxides presents far fewer difficulties in connection with the adhesion.

It has now been found that the presence of Al and Ti in the support is very detrimental to the adhesion of oxide layers obtained from triple carbonate, in particular when the cathodes are to supply a comparatively large current.

The invention will be described in greater detail with reference to the drawing, the sole FIGURE of which is a longitudinal sectional view through a cathode according to the invention.

Reference numeral 1 in the FIGURE denotes a cathode support consisting of nickel which has been obtained from carbonyl nickel to which a small quantity of reductors such as Mg and C has been added according to the powder metallurgical method. Said addition may be effected as is described in French Pat. Specification No. 1,152,810 by adding to the carbonyl nickel a given quantity of an alloy of nickel with the said reductors. The quantity of reductors in the ultimate alloy which serves for manufacturing the support is, for example, from 0.1 to 0.01 percent by weight for each re-.

ductor. It is ensured that the quantity of detrimental reductors Si, Al and Ti present as an impurity is less than 0.005 percent by weight. It has been found that an oxide layer formed from triple carbonate very readily adheres to such a support.

A heating member 3 is present in the support 1.

Although only one embodiment of a cathode according to the invention is shown, the invention is also of importance for so-called pot cathodes in which the emissive oxide layer is present on a closed end face of a cylindrical support. Such cathodes are suitable in particular for electron ray tubes, travelling wave tubes, klystrons and other tubes operating with beams of electron current and having a comparatively strongly loaded cathode (cathode current more than 1 amp. per cm of cathode area).

The cylindrical cathodes according to the drawing are very suitable for amplifier tubes which supply a comparatively large power, for example, ballast tubes and line output tubes for television apparatus.

What is claimed is:

1. An oxide cathode for an electric discharge tube, comprising a nickel support, a layer of emissive oxides provided on said support, said layer including a mixture of oxides of barium, strontium and calcium, said support being of nickel obtained according to the powdermetallurgical method and including reductors selected from the group consisting of magnesium and carbon, said nickel having the content of impurity selected from the group consisting of silicon, aluminum, titanium and chromium, lower than 0.005 per cent by weight to increase adhesion of said layer to said support. 

1. AN OXIDE CATHODE FOR AN ELECTRIC DISCHARGE TUBE, COMPRISING A NICKEL SUPPORT, A LAYER OF EMISSIVE OXIDES PROVIDED ON SAID SUPPORT, SAID LAYER INCLUDING A MIXTURE OF OXIDES OF BARIUM, STRONTIUM AND CALCIUM, SAID SUPPORT BEING OF NICKEL OBTAINED ACCORDING TO THE POWDER-METALLURGICAL METHOD AND INCLUDING REDUCTORS SELECTED FROM THE GROUP CONSISTING OF MAGNESIUM AND CARBON, SAID NICKEL HAVING THE CONTENT OF IMPURITY SELECTED FROM THE GROUP CONSISTING OF SILICON, ALUMINUM, TITANIUM AND CHROMIUM, LOWER THAN 0.005 PER CENT BY WEIGHT TO INCREASE ADHESION OF SAID LAYER TO SAID SUPPORT. 